How do I extract the specific values from NDVI time serie?

2 次查看（过去 30 天）
Devendra
Devendra 2024-4-5
回答： Suraj Kumar 2024-9-9
I have generated ndvi input file time series over crop season(1 year period) and want to extract the following; POS value;MAX sum;AVG sum;SOS;POS;EOS The discription of above mentioned parameters are as follows; (a) Phenological markers • Start of season (SOS): the date of growth start and crop emergence • Peak of season (POS): the date of the maximum NDVI value in the time series • End of season (EOS): the date of the harvesting and chlorophyll ab- sence • POS value: maximum NDVI value in the time series •
Average sum: sum of average NDVI values in the time series
• Maximum sum: sum of maximum NDVI values in the time series
• Base: the range between minimum and maximum NDVI
I am attaching input ndvi file as excel csv file. I am also attaching the output file as a sample it has not been derived from the above mentioned two input files. This is just sample output file. I am requesting to matlab signal processing comunity to please suggest me how to write this code. I would be highly obliged for any kind help.
Jyoti

请先登录，再回答此问题。

回答（1 个）

Suraj Kumar
Suraj Kumar 2024-9-9
Hi Devendra,
From what I understand, you are trying to extract specific phenological values from an NDVI time series using MATLAB.
For this you can refer to the following steps and the attached code snippets:
You can start by importing your NDVI data from the CSV file into MATLAB and then extract the dates and the NDVI values from the dataset.
% Load NDVI data from CSV
data = readtable('ndvi_time_series_input.csv');
% Extract dates and NDVI values
dates = data.Properties.VariableNames(2:end);
ndvi_values = data{:, 2:end};
Initialize the arrays using ‘NaT’ function in MATLAB, to store the desired results.
sos = zeros(size(ndvi_values, 1), 1);
pos = zeros(size(ndvi_values, 1), 1);
eos = zeros(size(ndvi_values, 1), 1);
pos_value = zeros(size(ndvi_values, 1), 1);
avg_sum = zeros(size(ndvi_values, 1), 1);
max_sum = zeros(size(ndvi_values, 1), 1);
base = zeros(size(ndvi_values, 1), 1);
Calculate the phenological markers by looping through each row of the NDVI data.
% Loop through each row in the NDVI data
for i = 1:size(ndvi_values, 1)
[pos_value(i), pos_idx] = max(ndvi_values(i, :));
pos(i) = datenum(dates{pos_idx}, 'yyyymmdd');
sos_idx = find(ndvi_values(i, :) > (min(ndvi_values(i, :)) + 0.1 * (pos_value(i) - min(ndvi_values(i, :)))), 1);
if ~isempty(sos_idx)
sos(i) = datenum(dates{sos_idx}, 'yyyymmdd');
end
eos_idx = find(ndvi_values(i, pos_idx:end) < (min(ndvi_values(i, :)) + 0.1 * (pos_value(i) - min(ndvi_values(i, :)))), 1);
if ~isempty(eos_idx)
eos(i) = datenum(dates{pos_idx + eos_idx - 1}, 'yyyymmdd');
end
avg_sum(i) = sum(ndvi_values(i, :)) / length(ndvi_values(i, :));
max_sum(i) = sum(max(ndvi_values(i, :)));
base(i) = range(ndvi_values(i, :));
end
Compile these calculations into a table for easy analysis and interpretation and display the results.
results = table(data{:, 1}, sos, pos, eos, pos_value, avg_sum, max_sum, base, ...
'VariableNames', {'Location', 'SOS', 'POS', 'EOS', 'POS_Value', 'Avg_Sum', 'Max_Sum', 'Base'});
disp(results);
You can look at the output for a better understanding:
For more details on the ‘NaT’ or ‘datenum’ functions in MATLAB, you can refer to the following links:
Happy coding!

类别

在 Help Center 和 File Exchange 中查找有关 Calendar 的更多信息

标签

产品


版本

R2024a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by